Torque preselecting mechanism



July 2, I946.

TORQUE PRESELEGTING MECHANISM Filed Aug. 17, 1943 w. P. LEAR 3/ 1'7 4% M J! V7! 023 J0 I v INVENTOR. lV/Z 1/4 2. 15M

A TTORNEY 2 Sheets-Sheet I July 2, 1946.

w. P. LEAR 2,403,094

TORQUE PRESELECTING MECHANISM Filed Aug. 17, 1943 2 Sheets-Sheet 2 INVENTOR. lV/[l/AM I. 164/? MQM ATTORNEY Patented July 1946 TORQUE PRESELECTING MECHANISM William P. Lear, North Hollywood, calls, assignor, by mesne assignments, to Leanlnoorporated, Grand Rapids, Mich., a corporation of Illinois Application August 17, 1943, Serial No. 499,610

' 7 Claims. 1

This invention relates to a torque transmitting but had no provision for preventing overdrive of the driven parts after deenergization of the power drive means, whereby further undetermined power was imparted to the load. Other types of torque limiting devices have relied upon the slippage between a pair of friction clutch faces to control the amount of torque. As clutch faces wear after a certain amount of use and, even initially, are not uniform in their coefiicients of friction, there resulted as wide variation in the limiting torque value in successive operations of the driving mechanism.

As a specific application, the invention is particularly useful with power driven tools such as power screw-drivers and power wrenches. 'In numerous cases, screws or bolts must be tightened to a predetermined torque factor, as in aircraft structures. Hitherto it has generally been necessary for an inspector to test each such fastening member and "experimentally" drive it home properly; at best a time consuming job and delaying factor in assembly line operations. With the present invention a continuously accurate torque limiting arrangement is provided in which there is no overdrive of the driven element when the power means is deenergized. Thus, a series of fastening elements, such as screws or nuts may be driven home directly with substantially a-nism having'a novel and accurate torque limiting arrangement including an abrupt acting clutch for disconnecting the power drive means from the driven member when the torque reaches its predetermined limiting value; to provide a torque transmitting mechanism including a high speed electric motor, a, quick acting electromagnetic clutch, and means for deenergizing the motor and clutch when the torque exerted on a member driven thereby reaches a predetermined limiting'vaiue; to provide a power driven tool including means for accurately preselecting the amount of torque exerted by the tool element; and to provide a simple reliable and accurate arrangement for limiting the amount of torque applied to a driven member.

These and other objects, advantages and features of the invention will be apparent from the following description and accompanying drawings. In the drawings:

Fig. i is an elevation view partly in section of a general embodiment oi the invention.

Fig. 2 is a crossmctionai view taken on the line 2--2 of Fig. 1.

mg. 3 is a cross sectional view taken on the line ilk-8 of Fig. 1.

Fig. 42 is an elevation view, partly in section of a power driven tool embodying the invention.

Fig. 5 is a plan view 0:? a torque limit switch included in the tool illustrated in Fig. 4.

Fig. 6 is an elevation view of a torque limiting element forming part of the power driven tool illustrated Fig. 4.

According to the present invention, a torque transmitting mechanism is provided, including a power driving means connected through a novel. clutch and gearing to a driven member. clutch is adapted to be abruptly effective simultaneously with energisation of the power driving means or with the deenergization of the power driving means. A particularly low inertia driven member minimizes any lag overshooting action by the clutch. ,The gearing includes a normally stationary movable member, which, when a predetermined torque is exerted upon the driven member, moves to sheet immediate deenergization of the power driving means and abrupt actuation of the clutch. Preferably, the clutch includes braking means for substantially instantaneously stopping motion of the driven member when the power driving means is decnergized.

Referring more particularly to Figs. 1, 2 and 3, a torque transmitting mechanism is illustrated comprising an electric motor l0 connected through an abruptly acting electromagnetic clutch l5 and reduction gearing 20 to a driven member 25. Electromagnetic clutch I5 is of the type described in my Patent No. 2,267,114 of December 23, 1941 for Electromagnetic clutch,

assigned to the same assignee as this case. It includes a. driving member H keyed to the motor drive shaft l2, and a low inertia driven member I3 connected to'the gearing 20. The-clutch is f mounted in a housing l4 secured to the casing of motor l3. Members II and II are made of magnetic material and an energizing winding i3 is cult relation with motor 13. The necessary elecprovided for eifecting magnetic and frictional coaction of the members II and i3. Member I3 is mounted in a bearing II in housing I4 and mediately urges member l3 into engagement with a braking surface 22 to effect quick stopp e of the driven member 23. Member 13 terminates in a driving pinion 23 forming part of gearing 23.

Gearing 23 includes a normally stationary movable gear carrying member 24 disposed in housing l4. As shown more particularly in Fig. 2, housing I4 is provided with an opening 23.' The portion of member 24 adjacent this opening is formed with gear teeth 21.. Gear teeth 21 cooperate with the teeth on gear sector 23 forming part of a switch mechanism 33 mounted inan extension 3| of housing 14. Switch mechanism 33 will be described hereinafter.

A plurality of shafts 32, which maybe three in number in the present instance. are mounted on member 24. Sleeves 33 are rotatablymounted on shafts 32 and fixed to each sleeve is a pinion 34. Each pinion 34 is a double pinion comprising a relatively large pinion gear 33 meshing with driving pinion 23, and a relatively small pinion gear 33 meshing with anintemal ring ear 31. The coaction between .pin'ion gears '33 and ring gear 31 is best illustrated in Fig. 3. The opposite endsof shafts 32 are supported in a plate 33.

I Gears 33 may be formed integrally with sleeves 33. Ring gear 31 is rotatably mounted on bearing 43 in the housing M. The ring gear includes 'a dial: portion 4| formed with a hub 42 mounted in-Joearing 43 in an end plate 44 for housing l4. Hub 42 is connected to flexible shafting '43- ing ear'33 in the extension. Shaft 41 is threaded as at 3| and provided with a lock nut 32. A spring 33 normally urges sector 23 away from ear or ing 33. Threaded portion 3! of shaft .41 provides for axial adjustment of gear'seotor 23. The upper end of gear sector 23 is adapted to engase either of a pair of limit switches 34, 33 which are included in the circuit or motor in and clutch l3. Asuitable weight 33 maybe mounted on the upper end ofgear sector 23 to increase its sensitivity of movement.

Sector 23 is normally urged to a vertical position by means of adjusting'means 31 and 33. Each adjusting means includes a spring 33 extending between a spring seat" on sectoril' .and a spring seat 32 on a'threaded shaft '33.-

clutch ll and gearing 23 on flexible shaftingjll.

The operation of the device isas follows. Mo-

and'clutch 13 are connected in on-oir circult and for rotation in either a clockwise or a counter-clockwise direction through switches 34. 33 and circuit means in terminal 31-. Clutch l3 is'connectedin series or paral l eficirtrical connections between motor H and clutch l3 are made in terminal box 31. .Manual starting and stopping of motor III is effected by a. switch (not shown) connected to cable 38 which enters terminal'box 31. Accordingly, when motor 13 is energized through closure of its circuit, winding I3 is likewise energized to cause abmpt' magnetic and frictional coaction between clutch elements H and I3. This instantly connects motor shaft l2-to drive pinion 23. Mounting member 24 is normally stationary. Accordingly, rotation of pinion 23 will effect rotation of gears 34 and thusof ring gear 31. Therefore, the torque exerted by'motor I3 is transmitted to flexible shafting 43. Adjusting means 31, 33 will previouslyhave been set to restrain movement of gear sector 23 until the amount of torquev exerted on shafting 43 reaches a. preselected value.

Mounting member 24. when torque is being transmitted from pinion 23 to shafting 43, is continually urged to movement in one direction or the other. The sole restraining force is gear sector 23 and adiusting means 31, 33. Hence, when such preselected value of maximu'm torque isv reached, the restraint is insuflicien-t to prevent movement of mounting member 24. As this member moves in one direction'or the other gear sector 23 is oscillated about itsishaft 41 to compress One or the other of the springs 33. The upper end of the gear sector engages the actuating plunger 33 or 33 of the limit switches 34 or 33. The associated switch operates to openthecircuit of motor l3 and clutch l3. The circuit of motor 13 being opened. the motor no longer exerts driving torque. and due to deenergization of clutch l3, its elements II and i3 abruptly separate under the influence of wring 2|. Low inand supported at its opposite end in an upstand I ertla clutch disk I3 is snapped into engagement with braking surfaceifl by spring 2|. This action substantially taneously stops movement of flexible shafting 43. There is thus no overdrive of shafting 43. This results in accurate torque limit control. 7

The described torque limiting system is soon-- rate and reliable in operation. It will be noted that mechanical clutch slippage is not relied upon for any function in the torque limiting action.

The torque limiting action is provided by adJust-.

ing means 31 and 33 which, in effect, restrain movement of mounting member 24. These ad- I the torque limiting means in successive operations. Due to the abrupt actuation of clutch l3 and the immediate enmement of low inertia driven disk l3'wlth braking surface 22, them-is overdrive. The device thus accurately limits the applied torque.

The device is capable of numerous applications. It is particularly applicable to motor actuated aircraft accessories, such as oil intercooler shutters, bomb bay doors. retractable landing gears, etc. In such applications. the device is preset to As a-number or elements'illustrated'in Fig. 4

are the same as the corresponding elements in primed have been used-to indicate the same or corresponding parts.

In the hand tool o'f Figs. 4, 5, and 6, electric motor I" drives a pinion 28'through the medium of electromagnetic clutoh li'. A mall high speed motor I0 is preferredin order to obtainthe proper power with minimum bulk and weight for the hand tool. The electromagnetic clutch II is of the same type asIS of Fig. 1, and is connected in series or parallel relation with the motor I0 so that it is energized when the motor circuit is closed, and is abruptly deenerglzed when the motor circuit is opened. The movable gear carrying member 24' differs somewhat from the member 24 of Figs. 1 and 2, as shown more particularly in Fig. 6. Instead of being formed with gear teeth, as in'the first embodiment, a pin I0 is threaded into member 24' and a roller II is ing 11. and has-a cam surface 8I engaged by roller I I.

tinually tends to rotate in housing 14'. Such rotation is resisted by spring 88 acting on arm 13 which is secured to pin I0 on member 24'. Howchuck I00. At the same time, spring 2| snaps clutch element I3into engagement with braking surface 22'; this Prevents any overdrive of chuck I00 and screw-driver H0, and results in accurate torque control. The torque limiting adjustment is accurate for successive actuations as there are substantially no wearing parts to change the setting of the torque adjustment. Hence, a number of screws may be driven home by screw-driver.

I I II with the same amount of maximum torque being exerted thereon in each instance. I

While specific embodiments of the invention have been shown and described to illustrate the application of the principles thereof, it will be Cam I8 is in operative relation with a plunger 82 of a limit switch 83 incorporated in the motor control switch which is operated by the button 84 projecting outside housin 11. The torque adjusting means in this instance comprises a spring seat 85 on a bolt 86 threaded through the wall of housing 11. A look nut 81 is provided to maintain bolt 86 in its adjusted position. Spring 88 extends between seat 85 and a spring seat 80 on arm I3. A stop pin 9| is provided toa tool receiving chuck l00. For this purpose. a-

fixed gear carrying plate 83 is provided in the housing I4 and a plurality of pinions 94 are mounted on member 93 in the same manner as pinions 34' are mounted on member 24. Each pinion 84 includes a relatively large pinion gear 96 and a relatively small pinion gear 81; Gears 06 engage drivin pinion 92 and gears 91 engage,

ring gear 90. A supporting bracket or plate IOI is provided to receivethe opposite ends of shafts I02 on which gears 94 are rotatably mounted. Ring gear 88 is mounted in bearing I03 in housing I4 and includes a disk member I04 which is formed with a hub I05 mounted in' a bearin I06 in the end wall 44' of housing I4. Hub I05 acts as a tool receiving chuck I00. It is adapted to interchangeably receive different driving tools such as screw-drivers, wrenches. and so forth. As illustrated, a screw-driver H0 is received in chuck I00 and retained therein by a snap ring The operation of t s power driven tool is the same as that previously described. Adjusting means 86 is set for the predetermined value of maximum torque to be exerted on screw-driver H0. The adjustment is then locked by nut 81. During power transmission from motor I0 to chuck I00, movable mounting member 24" con- ,said driven member understood that the invention may be otherwise embodied withoutdeparting from such principles.

I claim:

1. Torque limiting apparatus comprising an electric motor; a driving pinion operatively associated with said electric motor; a driven member; reduction gearing connected to said driven member and including an internal ring gear connected to said driven member, a normally stationary gear carrying member oscillatable rotatably mounted on said gear carrying member and meshed with said driving pinion and said ring gear; adjustable resilient means biasing said gear carrying member against movement; said gear carrying member moving when the torque on reaches a predetermined amount; an electromagnetic clutch having a driving-element connected to said electric motor and a driven element connected to said driving pinion, said clutch being connected in circuit relation with said motor and energized simultaneousl therewith; a housing enclosing said gearing; switch means mounted in said hous ing and connected in the circuit of said motor and said clutch; and a device operatively associated with said gear carrying member, and effective upon movement thereof to open said switch means to deenergize said motor and said clutch.

2. Torque limiting apparatus comprising an electric motor; a driving pinion operatively associated with said electric motor; a driven member;

gearing connected to said driven member and including an internal ring gear connected to said 3 driven member. a normally stationary gear carrying member oscillatable through a small arc and a plurality of pinions rotatably mounted on said gear carrying member and meshed with said driving pinion and said ring gear; adjustable resilient means biasing said gear carrying member against movement; said gear carrying member moving when the torque on said driven member reachesa predetermined amount; an electromagnetic clutch having a driving element connected to said electric motor and a driven element connectedto said driving pinion. said clutch being connected in circuit relation with said motor and energized simultaneously therewith; a housing enclosing said gearing; switch means mounted in said housing and connected in the-circuit of said 1 motor and switch clutch; a device operatively as- 7 sociated with said gear carrying member and effective upon movement thereof to open said switch means to'deenergize said motor and said clutch; a braking surface; andmeans'abruptly urging said driven element into engagement with said braking surface upon deenergization of said clutch to prevent overdrive and effect an accurate torque limitation on said driven memmounted on said plate and meshed with said driving pinion and said ring gear, said plate oscillating. about the axis of said driving pinion and driven member when the torque on said driven member reaches a predetermined amount; an electromagnetic clutch-brake unit including a clutch having a driving element connected to said ring gear; adjustable resilient means biasing said gear carrying member against movement; said gear carrying member moving when the torque on said chuck exceeds a predetermined amount; an electromagnetic clutch-brake unit including a clutch having a driving element connected to said electric motor and a driven element connected to said driving pinion, said clutch being connected in circuit relation with said motor and energized simultaneously therewith; and a device operatively associated with said gear carrying member and effective on movement thereof to immediately interrupt the energization of said electric motor and to simultaneously deenergize said clutch and engage said brake to abruptly stop motion of said chuck.

4. A power driven tool comprising, in combina-v tion, an electric motor; a chuck adapted to interchangeably receive tool elements; a driving pinion operatively associated with said electric motor; gearing operatively associated with said chuck and including an internal ring gear indriving relation with said chuck, a-normally stationary gear carrying member oscillatable through a small arc and a. plurality of pinions rotatably mounted on said gear carrying member and'meshed with said driving pinion and said ring gear; adjustable resilient means biasing said gear carrying member againstmovement; said gear carrying member moving when the torque 'on said chuck exceeds a predetermined amount;

an electromagnetic clutch having a driving element connected to said electric motor and a driven element connected to said driving pinion, said clutch being, connected in circuit relation with said motor and energized simultaneously therewith; a device operatively associated with said gear carrying member and effective on movement thereof to immediately interrupt'the energization of said electric motor and to simultaneously deenergize said clutch; a, braking surface: and means urging said driven element into engagement with said braking-surface upon deenergizationof said clutch to abruptly stop motion of said chuck.

5. A torque transmitting mechanism comprisin combination, an electric motor; a driving pinion operatively associated with said electric motor; a casing secured to said motor and having an opening; a driven member; reduction gearing mounted in said casing and connected to said driven member, said gearing including an internal ring gear connected .to said driven member, a gear carrying plate disposed adjacent said ope ng and a plurality of pinions rotatably electric motor and a low inertia driven element connected to said driving pinion, said clutch being connected in circuit relation with said motor and energized simultaneously therewith; a switch housing on said casing-adjacent said opening;

switch means mounted in said housing and connected in the circuit of said motor and said clutch; a switch operator operatively associated with said plate and said switch means and eflective to open said switch means in response to oscillation of said plate, to deenergize said motor and clutch and engage said brake to instantly stop motion of said driven member; and adjust able means restraining opening of said switch means.

6. A torque transmitting mechanism comprising, in combination, an electric motor; a driving pinion oper'atively associated with said electric motor; a casing secured to said motor and having an opening; a driven'member; reduction gearing mounted in said casing and connected to said drivenmember, said gearing including an internal ring gear connected to said driven member, a

gear carrying plate disposed adjacent said opening and a plurality of pinions rotatably mounted on said plate and meshed with said driving pinion and said ring gear, said plate oscillating about the axis of said driving pinion and driven member when the torque on said driven member reaches a predetermined amount, an electromagnetic clutch having adriving element connected to said electric motor and a low inertia driven element connected to said driving pinion, said clutch being connected in circuit relation with said motor and energized simultaneously therewith; a switch housing on said casing adjacent said opening; switch means mounted in said housing and connected in the circuit of said motor and said clutch; a switch operator operatively associated with said plate and 'said'switch means and effec-- tive to open said switch means in response to oscillation of said plate, to deenergize said motor and clutch; adjustable means restraining opening of said switch means; a braking surface; and

means abruptly urging said driven element into engagement'with said braking surface upon deenergization of said clutch to prevent overdrive of said drive member.

7. A power driven tool comprising, in combination; an electric motor; a driving pinion operatively associated with said electric motor; a casing secured to said motor and having an openin a driven pinion; a chuck adapted to interchangeplurality of pinions rotatably mounted on said movable plate and meshed with said driving pinion and said second internal ring gear: an electromagnetic clutch having a driving element con-- 9 nected to said electric motor and a low inertia driven element connected in said driving Pini said clutch being connected in circuit relation with said motor and energized simultaneously therewith; a switch housing on said casing adjacent said opening; switch means mounted; in said housing and connected in the circuit of said motor and said clutch; a switch operator operatively associated with said movable plate and 10 switch means and elective to open said switch means. in response to oscillation of said movable plate, to deenergize said motor and clutch; adjustable means restraining ope of said switch means; a braking surface; and means abruptly urging said driven element into engagement with said braking surface upondeenergizetion of said clutch to abruptly stop motion of said chuck.

' WILLIAM P. LEAR. 

